Flexible printed circuit board

ABSTRACT

A flexible printed circuit board includes a base layer and a pattern line. At least one communication hole penetrating opposite surfaces of the base layer. The pattern line includes two conductive circuit layers formed on the opposite surfaces of the base layer. At least one conductive pole are formed in the at least one communication hole and electrically connects the two conductive circuit layers. A gap being is formed between the conductive pole and the base layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of patent application Ser. No. 16/051,107 filed on Jul. 31, 2018, which is based on and claims priority to China Patent Application No. 201710949319.2 filed on Oct. 12, 2017, the contents of which are incorporated by reference herein.

FIELD

The subject matter herein generally relates to a flexible printed circuit board (FPCB).

BACKGROUND

FPCBs define holes to receive conductive posts. The conductive post electrically connects to other electrical element by a pad. To make a good contact between the conductive post and the pad, the FPCB further defines ring holes communicating with the receiving holes. An outer diameter of the ring hole is greater than a diameter of the receiving hole, causing layout problems on the FPCB.

Accordingly, there is room for improvement within the art.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by way of example only, with reference to the attached figures.

FIG. 1 is a flowchart of an exemplary embodiment of a method for manufacturing a FPCB.

FIG. 2 is a diagram of an embodiment of a substrate.

FIG. 3 is a diagram showing at least one connecting hole defined in the substrate of FIG. 2.

FIG. 4 is a diagram showing a first photosensitive film and a second photosensitive film on opposite surfaces of the substrate of FIG. 3.

FIG. 5 is a diagram showing the first photosensitive film and the second photosensitive film of FIG. 4 subjected to exposure and development.

FIG. 6 is a diagram showing a conductive pattern layer formed on the substrate of FIG. 5.

FIG. 7 is a diagram showing the first photosensitive film and the second photosensitive film of FIG. 6 peeled off.

FIG. 8 is a diagram showing the substrate of FIG. 7 after a etching treatment.

FIGS. 9A and 9B is a flowchart of another embodiment of a method for manufacturing a FPCB.

FIG. 10 is a diagram showing two single panels covering the surface of the two conductive circuit layers of FIG. 8.

FIG. 11 is a diagram showing through holes defined in the single panels of FIG. 10.

FIG. 12 is a diagram showing a third photosensitive film on a side of the single panel of FIG. 11.

FIG. 13 is a diagram showing the third photosensitive film of FIG. 11 subjected to exposure and development.

FIG. 14 is a diagram showing an outer conductive pattern layer formed on the single panel of FIG. 12.

FIG. 15 is a diagram showing the third photosensitive film of FIG. 13 peeled off.

FIG. 16 is a diagram showing the outer copper layer of FIG. 14 after a etching treatment.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the embodiments described herein. The drawings are not necessarily to scale and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure.

The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean “at least one.”

The term “comprising,” when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series, and the like.

Referring to FIGS. 1 to 8, a method for making a FPCB 100 is presented in a first embodiment. The method for making the FPCB 100 is provided by way of example, as there are a variety of ways to carry out the method. The method can begin at step 1.

At step 1, referring to FIGS. 1 and 2, a substrate 10 is provided. The substrate 10 includes a base layer 11 having two opposite surfaces and a first copper foil layer 12 is formed on one surface and a second copper foil layer 13 is formed on the opposite surface of the base layer 11.

In at least one embodiment, the base layer 11 is made of a polymer selected from a group consisting of polyimide, polyethylene terephthalate, and polyethylene naphthalate, and any combination thereof.

At step 2, referring to FIGS. 1 and 3, at least one connecting hole 102 is defined in the substrate 10.

In at least one embodiment, the substrate 10 defines two connecting holes 102. Each connecting hole 102 penetrates only the first copper foil layer 12 and the base layer 11. Each connecting hole 102 can be created using a laser. The connecting hole 102 includes a communication hole 104 penetrating the first copper foil layer 12. In another embodiment, each connecting hole 102 penetrates only the second copper foil layer 13 and the base layer 11. Each connecting hole 102 is mechanically cut.

At step 3, referring to FIGS. 1 and 4, a first photosensitive film 21 and a second photosensitive film 23 are pressed on surfaces of the substrate 10. The first photosensitive film 21 covers the first copper foil layer 12 and fills the connection hole 102. The second photosensitive film 23 covers the second copper foil layer 13.

At step 4, referring to FIGS. 1 and 5, the first photosensitive film 21 and the second photosensitive film 23 are subjected to exposure to form a first pattern 210 on the first photosensitive film 21 and the second photosensitive film 23. The first pattern 210 includes a positioning via 211 corresponding to the connecting hole 102 that exposes the second copper foil layer 13. An axis line of the positioning via 211 coincides with an axis line of the connecting hole 102. A diameter of the positioning via 211 is less than a diameter of the connecting hole 102. The first pattern 210 further includes a line pattern 213. The line pattern 213 is formed on the second photosensitive film 23 and on the photosensitive film 21 beside the positioning via 211.

At step 5, referring to FIGS. 1 and 6, the first pattern 210 is plated with copper to form a conductive pattern layer 31. The conductive pattern layer 31 includes a conductive pole 311 infilling the positioning via 211. The conductive pattern layer 31 further includes a first pattern line 313 formed on a surface of the first copper foil layer 12 away from the base layer 11 and a surface of the second copper foil layer 13 away from the base layer 11. The first pattern line 313 is corresponding to the line pattern 213.

At step 6, referring to FIGS. 1 and 7, the first photosensitive film 21 and the second photosensitive film 23 are peeled off to expose regions of the first copper foil layer 12 and a second copper foil layer 13 not covered with the conductive pattern layer 31.

At step 7, referring to FIGS. 1 and 8, perform a rapid etching treatment on the substrate 10 to remove the exposed regions so that the first copper foil layer 12 and the second copper foil layer 13 are respectively formed into a first conductive pattern layer 120 and a second conductive pattern layer 130. The rapid etching treatment etches only in a lamination direction of copper layers of the substrate 10. The first conductive pattern layer 120, the second conductive pattern layer 130, and the conductive pattern layer 31 form a pattern line 30. That is, the pattern line 30 includes two conductive circuit layers 301 on opposite surfaces of the base layer 11 and the conductive poles 311. The conductive poles 311 are used to electrically connect the two conductive circuit layers 301. One conductive circuit layer 301 is composed of a first conductive pattern layer 120 and a first pattern line 313 covering the first conductive pattern layer 120, and another conductive pattern layer 130 and a first pattern line 313 cover the second conductive pattern layer 130.

In another embodiment, before defining the connection hole 102 on the substrate 10, the copper subtract can be subjected to a thinning process as needed to render a uniform thickness to the first bottom copper layer 12 and to the second bottom copper layer 13.

In another embodiment, a cover film (not shown) is formed on the pattern line 30 and the base layer 11, and the cover film fills the communication hole 104.

Referring to FIG. 8, the FPCB 100 manufactured by the method above includes the base layer 11 and the pattern line 30. The base layer 11 defines at least one communication hole 104 penetrating opposite surfaces of the base layer 11. The pattern line 30 includes two conductive circuit layers 301 formed on opposite surfaces of the base layer 11, and the conductive pole 311 formed in the communication holes 104 which electrically connects the two conductive circuit layers 301. The diameter of the conductive pole 311 is smaller than the diameter of the communication hole 104.

Referring to FIGS. 8 to 16, in another embodiment, the method further includes following steps.

At step 8, referring to FIGS. 9 and 10, a single panel 40 covers a surface of the at least one conductive circuit layer 301 away from the base layer 11.

In this embodiment, a single panel 40 covers each of the surfaces of the two conductive circuit layers 301 away from the base layer 11. Each single panel 40 includes an outer copper layer 41 and an adhesive layer 42 adhered between the outer copper layer 41 and the conductive circuit layers 301. The adhesive layer 42 covers the pattern line 30 and the base layer 11, and infills the communication hole 104.

At step 9, referring to FIGS. 9 and 11, at least one through hole 402 is defined in the at least one single panel 40 to expose the pattern line 30. The through hole 402 includes a through hole 404 penetrating the adhesive layer 42.

In this embodiment, the through hole 402 is formed on the single panel 40 adjacent to the first conductive pattern layer 120 corresponding to the conductive pole 311. The through hole 402 exposes the conductive pole 311. The through hole 402 can be created using a laser.

In another embodiment, the through hole 402 is defined in the pattern line 30 except for the conductive pole 311. The through hole 402 is formed by other processing methods, such as being mechanically cut.

At step 10, referring to FIGS. 9 and 12, a third photosensitive film 51 is pressed on a side of the single panel 40 away from the substrate 10. The through hole 402 is infilled by the third photosensitive film 51.

At step 11, referring to FIGS. 9 and 13, the third photosensitive film 51 is developed by exposure to form a second pattern 510 on the third photosensitive film 51. The second pattern 510 includes a hole 512 corresponding to the through hole 402. A diameter of the hole 512 is smaller than a diameter of the through hole 402.

The second pattern 510 further includes a line pattern 513. The line pattern 213 is formed on the third photosensitive film 51 beside the hole 512.

At step 12, referring to FIGS. 9 and 14, the second pattern 510 is plated with copper to form an outer conductive pattern layer 61. The outer conductive pattern layer 61 includes a conductive post 611 infilled in the hole 512. The outer conductive pattern layer 61 further includes a second pattern line 613 formed on a surface of the outer copper layer 41 away from the adhesive layer 42. In this embodiment, the second pattern line 613 corresponds to the line pattern 513. The conductive post 611 is aligned with the conductive pole 311.

At step 13, referring to FIGS. 9 and 15, the third photosensitive film 51 after exposure is peeled off so that regions not covered by the outer conductive pattern layer 61 are exposed.

At step 14, referring to FIGS. 9 and 16, performing a rapid etching treatment on the outer copper layer 41 to remove the exposed regions. The outer copper layer 41 is thus formed into a third conductive pattern layer 410 corresponding to the outer conductive pattern layer 61, and thereby the FPCB 200 is formed. The graphics layer 410 is used to fabricate the FPCB 200. The third conductive pattern layer 410 and the second pattern line 613 constitute an outer conductive layer 601. The outer conductive layer 601 and the conductive post 611 constitute an outer pattern line 60.

In another embodiment, a cover film (not shown) is formed on the pattern line 60 and the adhesive layer 42, and the cover film infills the through hole 404.

Steps 10-16 can be repeated to obtain a FPCB having additional layers.

Referring to FIG. 16, the FPCB 200 is manufactured by the methods above. The FPCB 200 further includes one or two adhesive layers 42 and the outer pattern line 60. Each adhesive layer 42 covers one side of the pattern line 30 and the base layer 11 on the same side that is not covered by the pattern line 30. At least one adhesive layer 42 defines at least one through hole 404, penetrating the adhesive layer 42, to expose the pattern line 30. The outer pattern line 60 includes an outer conductive layer 601 formed on a surface of the adhesive layer 42 away from the base layer 11, and the conductive post 611 formed in the through hole 404 which electrically connects the outer conductive layer 601 to the pattern line 30. The diameter of the conductive post 611 is less than the diameter of the through hole 404.

Even though information and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the present embodiments, the disclosure is illustrative only. Changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the present embodiments to the full extent indicated by the plain meaning of the terms in which the appended claims are expressed. 

What is claimed is:
 1. A flexible printed circuit board comprising: a base layer defining at least one communication hole penetrating opposite surfaces of the base layer; a pattern line comprising two conductive circuit layers formed on the opposite surfaces of the base layer; and at least one conductive pole formed in the at least one communication hole and electrically connecting the two conductive circuit layers, a gap being formed between the conductive pole and the base layer.
 2. The flexible printed circuit board of claim 1, further comprising: an outer pattern line; a adhesive layer covering a side of the pattern line and the base layer on the same side that is not covered by the pattern line, the adhesive layer defining at least one through hole penetrating the adhesive layer to expose the pattern line; wherein the outer pattern line comprises an outer conductive layer formed on a surface of the adhesive layer away from the base layer, and the conductive post formed in the through hole and electrically connected to the outer conductive layer to the pattern line, a diameter of the conductive post is less than a diameter of the through hole.
 3. The flexible printed circuit board of claim 1, further comprising: an outer pattern line; two adhesive layers, each adhesive layer covering one side of the pattern line and the base layer on the same side that is not covered by the pattern line, at least one adhesive layers defining at least one through hole penetrating the adhesive layer to expose the pattern line; wherein the outer pattern line comprises an outer conductive layer formed on a surface of the adhesive layer away from the base layer, and the conductive post formed in the through hole and electrically connected to the outer conductive layer to the pattern line, a diameter of the conductive post is smaller than a diameter of the through hole.
 4. The flexible printed circuit board of claim 1, wherein the conductive post is aligned with the conductive pole.
 5. The flexible printed circuit board of claim 1, wherein the base layer is made of a polymer.
 6. A flexible printed circuit board comprising: a base layer defining at least one communication hole penetrating opposite surfaces of the base layer; a pattern line comprising two conductive circuit layers formed on the opposite surfaces of the base layer; and at least one conductive pole formed in the at least one communication hole and electrically connecting the two conductive circuit layers, a diameter of each conductive pole being smaller than a diameter of corresponding communication hole.
 7. The flexible printed circuit board of claim 6, further comprising: an outer pattern line; a adhesive layer covering a side of the pattern line and the base layer on the same side that is not covered by the pattern line, the adhesive layer defining at least one through hole penetrating the adhesive layer to expose the pattern line; wherein the outer pattern line comprises an outer conductive layer formed on a surface of the adhesive layer away from the base layer, and the conductive post formed in the through hole and electrically connected to the outer conductive layer to the pattern line, a diameter of the conductive post is smaller than a diameter of the through hole.
 8. The flexible printed circuit board of claim 6, further comprising: an outer pattern line; two adhesive layers, each adhesive layer covering one side of the pattern line and the base layer on the same side that is not covered by the pattern line, at least one adhesive layers defining at least one through hole penetrating the adhesive layer to expose the pattern line; wherein the outer pattern line comprises an outer conductive layer formed on a surface of the adhesive layer away from the base layer, and the conductive post formed in the through hole and electrically connected to the outer conductive layer to the pattern line, a diameter of the conductive post is smaller than a diameter of the through hole.
 9. The flexible printed circuit board of claim 6, wherein the conductive post is align with the conductive pole.
 10. The flexible printed circuit board of claim 6, wherein the base layer is made of a polymer. 